The Atmosphere and Climate Modeling - Introduction to Carbon Capture and Sequestration - page 74

18 O and

Box 2.4.1 δ δ D

18 O analysis is a technique used in geochemistry as a proxy for paleotemperatures.
This technique involves measuring the 18 O: 16 O ratio found, for example, in corals,
foraminifera and ice cores. It relies on the fact that water with 18 O has slightly different
properties than water with 16 O. A practical consequence is that the

δ

18 O value of
seawater correlates with the extent of polar ice sheets. Another consequence is that
the foraminifera shells of calcium carbonate have different 18 O: 16 O ratios depending
on the temperature of the water in which shells were formed. Similar observations
have been made for H (hydrogen) and D (deuterium), which is the basis determining
the D:H ratio. Scientists throughout the world employ enormously sensitive instru-
ments and considerable perspicacity in using isotopes to understand temperature
changes over geological ages.

δ

400 2000

1800

1600

350

1400

1200

300

1000

800

250 600

0 500 1000 1500 2000

Year

Figure 2.4.14 Concentration of the most important greenhouse gasses
Atmospheric concentrations of the important greenhouse gasses over the last 2,000
years, in units of parts per million (ppm) or parts per billion (ppb), indicate the number
of molecules of the greenhouse gas per million or billion air molecules, respectively, in
an atmospheric sample. Figure from IPCC, reproduced with permission [2.2].